JPH0739609B2 - Method for producing structural refractory steel material having strength of 60 kg or more excellent in high temperature strength property after reheating - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a tensile strength at room temperature which is used for a steel structure such as a building or a bridge which is likely to be in a high temperature state for a short time of about several hours due to fire or the like. 60kgf / mm ² The present invention relates to a method for producing a steel material, and more particularly, to a method for producing a structural fire-resistant steel material having excellent high-temperature strength properties after reheating, which can be reused after a high temperature is once caused by a fire or the like.

[0002]

2. Description of the Related Art Generally, structural steel materials are manufactured so as to have a sufficient predetermined strength at room temperature, but generally, the strength decreases as the temperature rises. In particular, the conventional structural steel material shows a marked decrease in strength in a high temperature state of about 500 ° C. or higher.
Are known. Therefore, in structures where there is a risk that the temperature will rise to a high temperature due to a fire, etc., especially in buildings where humans live, prevent the structures from collapsing or deforming significantly even under high temperature conditions. In order to secure the temperature, a fireproof coating is applied so that the temperature of the steel material does not rise significantly.

As a countermeasure against such existing fire resistance, if the strength reduction of the steel material can be suppressed to a small level even at high temperature, the thickness of the fire resistant coating can be reduced, or
It is possible to reduce other measures for fire resistance.

Regarding steel materials that guarantee strength at high temperatures,
Research has been conducted in the field of steel for pressure vessels,
For example, in the Japanese Industrial Standard (JIS), JIS G 3
124; It has already been standardized for high-strength steel plates for medium / normal temperature pressure vessels. Further, although not specifically defined, as a steel for a pressure vessel, which is premised on having high strength at medium and high temperatures exceeding room temperature, for example, in JIS, JIS G
3118; Carbon steel plate for medium / normal temperature pressure vessel, JIS G
3119; Manganese molybdenum steel and manganese molybdenum nickel steel plates for boilers and pressure vessels, JIS G
3120; tempered manganese molybdenum steel and manganese molybdenum nickel steel sheet for pressure vessels, JIS G 4
109; chrome molybdenum steel steel plates for boilers and pressure vessels. Further, Japanese Patent Publication No. 60-35985 discloses high strength and toughness steel for pressure vessels. The steel disclosed here is not limited to the characteristics at high temperatures, but is premised to have a certain degree of high-temperature strength as a pressure vessel steel.

However, in the case of such steel,
Usually, expensive alloy elements such as Cr and Mo are added in a large amount of 0.5% or more in order to increase the high temperature strength. It is generally done. In addition, JIS G 31
24; In the high-strength steel sheet for medium / normal temperature pressure vessels, the amount of alloying elements added is relatively small, but the strength at high temperature is regulated up to 400 ° C. That is, sufficient strength cannot be obtained at a considerably high temperature exceeding 400 ° C. Moreover, these steel materials are premised on steel materials for pressure vessels,
It cannot be said that it has sufficient properties as a structural steel material. Furthermore, when a fire occurs in a structure, the steel material is once in a high temperature state, so it is expected that the characteristics of the steel material will change, and when the structure is reused after the fire,
It becomes necessary to replace that part. Replacement of components is, of course, not desirable from an economical point of view.

[0006] A structural steel material having fire resistance is disclosed in Japanese Patent Application Laid-Open No. 2-77523, but the steel disclosed here has a high Mo addition amount of 0.4 to 0.7%. However, it is a high alloy type component as a structural steel material that is normally used. Furthermore, although Japanese Patent Laid-Open No. 2-77523 stipulates high-temperature strength characteristics up to manufacturing,
There is no indication of the properties of the steel once a fire has occurred, and it is difficult to reuse this steel after it has reached a high temperature.

Japanese Unexamined Patent Publication (Kokai) No. 2-254134 also discloses the content of refractory steel, but it is necessary to add Cr, Ni and Cu, and it is necessary to make a high alloy steel.
Tensile strength at room temperature is 60kgf / mm ² And less than sufficient strength is not secured. Further, nothing is shown about the high-temperature strength property after reheating, and it cannot be reused after reaching a high temperature state.

As described above, at room temperature, it is stable at 60 kgf / mm.
² It has the above strength and contains many alloy components such as Mo and Cr.
30kgf / mm without adding amount² High temperature yield strength
It is possible to secure the
Can guarantee excellent high-temperature strength properties even after being used and can be reused
Most structural fire-resistant steel materials that can withstand enough
The current situation is that it has not been developed. That is, the current question
The points are summarized below.

(1) A method for producing a steel material that satisfies the sufficient characteristics as a structural steel material (high weldability, high ductility, etc.) and maintains high high-temperature strength at about 400 ° C. or higher has not been established. . (2) In order to satisfy the characteristics of (1), a large amount of expensive alloy elements are added, so that the steel material cost is very high. (3) The normal temperature and high temperature characteristics of the steel material once deteriorated to a high temperature state cannot be reused.

The present invention has been made in view of the above circumstances, and retains high strength at high temperature without adding a large amount of expensive alloying elements, and is good even after once becoming high temperature. Can maintain or improve high-temperature strength properties, and has high weldability and high ductility, which are the advantages of conventional structural steels, and has a tensile strength at room temperature of 60 kgf / mm ² Above and 40 of conventional structural steel,
60kgf / mm ² which has higher room temperature strength than 50kg steel and excellent high temperature strength characteristics after reheating. It is an object of the present invention to provide a method for manufacturing a structural refractory steel material having the above strength.

[0011]

In order to achieve the above object, the present invention is, firstly, in terms of weight%, C: 0.05% or more and less than 0.20% Si: 0.1 % Or more and less than 2.0% Mn: 0.3% or more and less than 2.0% P: 0.03% or less S: 0.03% or less Mo: 0.1% or more and less than 0.4% Ti: 0.003% or more and less than 0.1% V: 0.01% or more and less than 0.1% sol. Al: 0.002% or more, less than 0.2% N: 0.0010% or more, less than 0.020%

When a steel containing Fe and the unavoidable impurities as the balance is heated to 1000 to 1350 ° C. and hot-rolled, the reduction rate is set to 30% or more at 900 ° C. or more, and the finishing temperature is Ar ₃ ~ Ar ₃ + 150 ℃, then immediately quench, or air-cooled and reheated to 880 ℃ or more, then quenched, then reheated to a temperature of 700 ℃ or less and air-cooled, high temperature after reheating 60kgf / mm ² with excellent strength characteristics Provided is a method for manufacturing a structural refractory steel material having the above strength. Secondly, in addition to the steel having the above composition, Cu: 0.01% or more and less than 1.5% Ni: 0.02% or more and less than 2.0% Cr: 0.05% or more, 1.5% Less than B: 0.0005% or more, less than 0.005% Nb: 0.005% or more, less than 0.05%

10 steels containing one or more of
When heated to 00 to 1350 ° C. and hot rolled,
And a reduction ratio of 30% or more at 900 ° C. or higher, after the finishing temperature and Ar ₃ ~Ar ₃ + 150 ℃, or immediately quenching or air cooling and reheating after quenching to 880 ° C. or higher, then 700 ° C. below the temperature 60kg with excellent high-temperature strength characteristics after reheating, characterized by being reheated to air and cooled in air
f / mm ² Provided is a method for manufacturing a structural refractory steel material having the above strength. Third, in% by weight, C: 0.05% or more and less than 0.20% Si: 0.1% or more and less than 2.0% Mn: 0.3% or more and less than 2.0% P: 0.03% or less S: 0.03% or less Mo: 0.1% or more, less than 0.4% Ti: 0.003% or more, less than 0.1% V: 0.01% or more, 0.1% Less than sol. Al: 0.002% or more, less than 0.2% N: 0.0010% or more, less than 0.020%

When a steel containing Fe and the unavoidable impurities as the balance is heated to 1000 to 1350 ° C. and hot-rolled, the reduction rate is set to 30% or more at 900 ° C. or more, and the finishing temperature is Ar ₃ ~ Ar ₃ +150 ℃, then immediately quench, or air-cooled and reheated to 880 ℃ or more and then quenched, then reheated to a temperature of 740 to 840 ℃, and then to a temperature of 700 ℃ or less. 60kgf / mm ² excellent in high temperature strength characteristics after reheating, characterized by reheating and air cooling Provided is a method for manufacturing a structural refractory steel material having the above strength. Fourth, in addition to the above composition of steel, Cu: 0.01% or more and less than 1.5% Ni: 0.02% or more and less than 2.0% Cr: 0.05% or more, 1.5% Less than B: 0.0005% or more, less than 0.005% Nb: 0.005% or more, less than 0.05%

10 steels containing one or more of
When heated to 00 to 1350 ° C. and hot rolled,
The reduction ratio was 30% or more at 900 ° C. or higher, the finishing temperature after the Ar ₃ ~Ar ₃ + 150 ℃, either immediately quenching or air cooling and reheating after quenching to 880 ° C. or more, the subsequent seven hundred forty to eight hundred forty ° C. It has excellent high-temperature strength characteristics after reheating, which is characterized by being reheated to a temperature and quenched, and subsequently reheated to a temperature of 700 ° C. or less and air-cooled.
0 kgf / mm ² Provided is a method for manufacturing a structural refractory steel material having the above strength.

In the present invention, the most important point is that, in consideration of weldability, cost, etc., the tensile strength at room temperature is 60 kgf / mm ² in the state where the steel material is manufactured. Is over,
And the high temperature yield strength at 600 ℃ is 30kgf / mm ² While having high temperature strength characteristics sufficiently high as above,
That is, it retains sufficient room temperature / high temperature strength properties even after it has reached a high temperature state.

In view of the above, the inventors of the present invention have conducted extensive studies to solve the above-mentioned problems, and as a result, hot-rolling under specific conditions is mainly performed on steel containing Mo, V, and Ti in combination. It has been found that by applying it, a sufficiently high room-temperature / high-temperature strength property can be imparted and the room-temperature / high-temperature strength property after reheating can be made sufficiently high. The present invention having the above contents is made based on the findings of the inventors of the present application. Next, the reasons for limiting the content of each additive element will be shown.

C: C is an effective element for stably ensuring the room temperature strength and high temperature strength of steel. But 0.0
If it is less than 5%, it is difficult to obtain a predetermined sufficient strength, and if it is 0.20% or more, the weldability deteriorates. Therefore, the content of C is specified to be 0.05% or more and less than 0.20%.

Si: Si is an element effective as a deoxidizing element, and it is necessary to add at least 0.1%. Further, Si is an element effective for solid solution strengthening, but 2.
If the addition amount is 0% or more, there are problems such as reduction in ductility and increase in inclusions. Therefore, the Si content is set to 0.
It is specified to be 1% or more and less than 2.0%.

Mn: Mn is an element effective in ensuring strength, and for that purpose, 0.3% or more is required to be added. If it is 2.0% or more, the weldability is deteriorated. Therefore, the Mn content is specified to be 0.3% or more and less than 2.0%.

P, S: P and S are impurity elements and cause problems such as a decrease in ductility, workability and weldability, so it is desirable to reduce them as much as possible. However, if it is significantly reduced, the cost will increase. For this reason, the content of these is specified to be 0.03% or less, which is a range in which the cost is not increased and the material is not significantly deteriorated.

Mo: Mo is an effective element for increasing the strength of steel by improving hardenability, precipitation strengthening, etc.
It is effective for medium and high temperature strength. However, 0.1%
If it is less than 1, it is difficult to obtain the effect, and if it is 0.
Addition of a large amount of 4% or more not only raises the cost but also deteriorates the weldability. Therefore, the content of Mo is 0.1% or more and 0.1.
Specify less than 4%.

V: V is an element that is effective not only for increasing the high temperature strength even when added in a small amount, but also for improving the room temperature / high temperature strength characteristics after reheating. However, if it is less than 0.01%, such an effect cannot be obtained, and addition of a large amount of 0.1% or more deteriorates the weldability and increases the cost. Therefore, the V content is specified to be 0.01% or more and less than 0.1%.

Ti: Ti has the effect of forming TiN and refining the austenite grains, and is effective in improving toughness, while solid solution Ti forms TiC in a high temperature state and also increases high temperature strength. Improves room temperature / high temperature strength and toughness after heating. However, if less than 0.003%, these effects cannot be obtained, and addition of a large amount of 0.1% or more deteriorates weldability. Therefore, the Ti content is 0.003
% Or more and less than 0.1%.

Sol. Al: sol. Al is an element that precipitates in the steel as AlN and is effective in refining the crystal grains. However, if it is less than 0.002%, the effect cannot be obtained, and if it is added in an amount of 0.2% or more, oxide-based inclusions increase, and ductility deteriorates. Therefore, sol. Al
Content of 0.002% or more and less than 0.2%.

N: N is an element for precipitating AlN or TiN, and is effective for refining crystal grains. But,
If less than 0.0010%, the effect cannot be obtained, and
If a large amount of 0.020% or more is added, the toughness of the welded portion deteriorates. Therefore, the content of N is 0.0010% or more and 0.0
Specify less than 20%.

Nb: Nb is an element effective not only in strength at room temperature but also in strength at high temperature. However, 0.
If it is less than 005%, the effect cannot be obtained.
%, The toughness of the weld will deteriorate. Therefore, the Nb content is specified to be 0.005% or more and less than 0.05%.

Cu: Cu is an element effective for solid solution strengthening, and if it is about 1% or more, precipitation strengthening can be expected. It is also effective for corrosion resistance. But,
If it is less than 0.01%, the effect cannot be obtained, and it is 1.5%.
In addition to the cost increase, the above additions have a problem of surface scratches on the steel sheet. Therefore, the Cu content is 0.01% or more and 1.5
Specify less than%.

Ni: Ni is an element effective in improving low temperature toughness. However, if it is less than 0.02%, its effect is small, and since Ni is expensive, the cost increase is remarkable if it is 2.0% or more. Therefore, the Ni content is specified to be 0.02% or more and less than 2.0%.

Cr: Cr is effective as a solid solution strengthening element, and is also effective for increasing the high temperature strength and corrosion resistance. However, if it is less than 0.05%, the effect cannot be obtained, and if it is 1.5% or more, the cost rises and the weldability deteriorates. Therefore, the content of Cr should be 0.05
% To less than 1.5%.

B: B is an effective element that increases the hardenability of steel by adding a trace amount, and if it is 0.0005% or more, it shows the effect sufficiently. Further, if it is 0.005% or more, the effect of improving the hardenability becomes small and the weldability deteriorates. Therefore, the content of B is 0.0005% or more and 0.0
Specify less than 05%. Next, the manufacturing process will be described.

First, 1000 to 1 of the steel having the above-mentioned chemical composition is prepared.
Heat to 350 ° C. This is because if the heating temperature is lower than 1000 ° C, it is impossible to secure a predetermined rolling end temperature, and if it exceeds 1350 ° C, the heating cost remarkably increases.

Then, hot rolling is performed. In this case, in order to obtain the desired characteristics, it is necessary to refine the austenite crystal grains, but for that purpose, it is necessary to sufficiently process the austenite recrystallization region, and at least 30%.
The above processing is required. From this point of view, the hot rolling conditions were such that the rolling reduction was 30% or more in the temperature range of 900 ° C. or higher which is the austenite recrystallization region.

[0034] is less than the rolling finishing temperature is Ar ₃ temperature, becomes a two-phase region rolling, in the case of immediately quenching after rolling, the hardenability is significantly reduced, it is difficult to secure a predetermined strength, Ar ₃ If the temperature exceeds + 150 ° C, the crystal grains become significantly coarse. Therefore, the finishing temperature is Ar _{3 to} A
Specified as r ₃ + 150 ° C.

It is possible to quench immediately from this temperature,
It is also possible to cool by air, reheat to 880 ° C. or higher, and then quench.
This is because when the reheating temperature is lower than 880 ° C., there is a possibility that the reheating temperature will be partially heated to the two-phase region, and the uniformity of the steel material properties will deteriorate.

After quenching, it is reheated to a temperature of 700 ° C. or lower and air-cooled. This is because if the temperature exceeds 700 ° C., the material may be partially heated in the two-phase region and the uniformity of the material may significantly change.

When a low yield ratio is required in the steel material for building structures, the above-mentioned quenching treatment and 700
It is necessary to add a step of reheating to a temperature range of 740 to 840 ° C. and quenching, in addition to reheating at a temperature of not higher than 0 ° C. When the reheating temperature at this time is 700 ° C. or higher, the yield ratio decreases, but the structure becomes nonuniform in the two-phase region below 740 ° C. On the other hand, if the temperature exceeds 840 ° C, the yield ratio cannot be lowered. Therefore, the reheating temperature range is set to 740 to 840 ° C. as a temperature range in which a uniform structure and material can be secured and the yield ratio can be lowered.

[0038]

Embodiments of the present invention will be described below.

Table 1 shows the chemical composition and Ar ₃ temperature of the test steel. Steels A to F are components / compositions within the scope of the present invention, and reference symbols G to I are comparative steels deviating from the components / compositions of the present invention. Comparative steels G, H, and I are steels of the present invention A,
Each of the comparative steels G and H does not contain V, which is an essential element in the present invention, although it has a component system corresponding to each of F and E.
In Comparative Steel I, V and Mo are outside the scope of the present invention.

Table 2 shows the production conditions of the steel sheets produced using the test steels A to I and the results of the room temperature tensile test and the high temperature tensile test. The high temperature tensile test was performed not only on the as-manufactured material but also on the steel material reheated to 600 ° C. In Table 2, the alphabets shown at the beginning of the reference numerals correspond to A to H in Table 1, and for example, when written as A-1, it indicates that the steel A shown in Table 1 was used.

Reference symbols A-1 to F-2 are examples satisfying the components / compositions and production conditions within the scope of the present invention, and reference symbols G, H, and I are the production conditions within the scope of the present invention. Is a comparative example in which the components and compositions are out of the range of the present invention.

As is clear from Table 2, in the case of all the examples, the tensile strength (TS) at room temperature was 60 kgf / mm ^{2 in} all cases. Further, the yield strength in the as-manufactured high temperature tensile test satisfies the requirement of 30 kgf / mm2 or more required by the present invention. The high temperature yield strength (YS) after reheating to 600 ° C is also 30 kgf / mm ² The above is higher than the as-manufactured high-temperature yield strength, confirming that the high-temperature strength properties after reheating are excellent.

On the other hand, G, H and I which are comparative examples
The manufacturing conditions are within the scope of the present invention, but the components / compositions are outside the scope of the present invention, and the tensile strength at room temperature is 60 kgf / mm ²
Although the above is satisfied, the corresponding Examples A-1 and F-
2, the high temperature strength is lower than that of E. In Comparative Examples H and I, the high temperature yield strength was 30 kgf / mm ² Is less than
The value required by the present invention is not satisfied. Furthermore, the high-temperature yield strength after reheating is lower than as-manufactured,
The high temperature strength properties after reheating are insufficient. In Comparative Example G, the high temperature yield strength was 30 kgf / mm ² as manufactured. As mentioned above, the high temperature yield strength after reheating is 30 kgf / mm ² It is less than the value and does not satisfy the value required by the present invention. Regarding the high temperature yield strength after reheating, H and I of the comparative examples are also 30 kgf.
/ Mm ² It was confirmed that the high temperature yield strength after reheating was insufficient in all Comparative Examples.

[0044]

EFFECTS OF THE INVENTION According to the present invention, many expensive alloy elements are contained.
30kgf / mm at high temperature without adding amount² More than
Maintains high yield strength and tensile strength at room temperature of 60kgf
/ Mm² Higher than above, and even after once becoming high temperature
Can maintain or improve good high temperature strength properties
High welding, which is an advantage of conventional structural steel
And a method for manufacturing structural fire-resistant steel with high ductility are proposed.
Be served. For this reason, fire resistance has been conventionally required.
Reduces the thickness of refractory coating that was naturally used in structures
In addition to the simplification of design and construction methods,
Other measures against fire can be reduced. Furthermore, at room temperature
Strength is 60kgf / mm² Compared to the above and conventional structural steel materials,
Since it is high, the thickness and weight of the steel materials used for the members are reduced.
It becomes possible to do.

[0045]

[Table 1]

[0046]

[Table 2]

Claims (4)

[Claims] 1. In% by weight, C: 0.05% or more and less than 0.20% Si: 0.1% or more and less than 2.0% Mn: 0.3% or more, less than 2.0% P : 0.03% or less S: 0.03% or less Mo: 0.1% or more and less than 0.4% Ti: 0.003% or more and less than 0.1% V: 0.01% or more, 0.1 Less than% sol. Al: 0.002% or more, less than 0.2% N: 0.0010% or more, less than 0.020%, with the balance being Fe and inevitable impurities 1
When heated to 000 to 1350 ° C. and hot-rolled, the reduction ratio is set to 30% or more at 900 ° C. or more, and the finishing temperature is set to Ar ₃ to Ar ₃ + 150 ° C., followed by immediate quenching or air cooling. It is excellent in high-temperature strength characteristics after reheating, which is characterized in that it is reheated to 880 ° C or higher and then quenched, then reheated to a temperature of 700 ° C or lower and air-cooled
A method for manufacturing a structural refractory steel material having a strength of not less than kg. 2. In weight% display, C: 0.05% or more and less than 0.20% Si: 0.1% or more and less than 2.0% Mn: 0.3% or more and less than 2.0% P : 0.03% or less S: 0.03% or less Mo: 0.1% or more and less than 0.4% Ti: 0.003% or more and less than 0.1% V: 0.01% or more, 0.1 Less than% sol. Al: 0.002% or more, less than 0.2% N: 0.0010% or more, less than 0.020% included Cu: 0.01% or more, less than 1.5% Ni: 0.02% or more , Less than 2.0% Cr: 0.05% or more, less than 1.5% B: 0.0005% or more, less than 0.005% Nb: 0.005% or more, less than 0.05% 1 type or When a steel containing two or more kinds and the balance consisting of Fe and unavoidable impurities is heated to 1000 to 1350 ° C. and hot-rolled, the reduction rate is set to 30% or more at 900 ° C. or more, and the finishing temperature is Ar ₃ ~ Ar ₃ +
After heating to 150 ° C, quench immediately or air cool 8
A structural refractory steel material having a strength of 60 kg or more excellent in high-temperature strength characteristics after reheating, which is characterized by being reheated to 80 ° C or higher and then quenched, and then reheated to a temperature of 700 ° C or lower and air-cooled. Production method. 3. In% by weight, C: 0.05% or more and less than 0.20% Si: 0.1% or more and less than 2.0% Mn: 0.3% or more, less than 2.0% P : 0.03% or less S: 0.03% or less Mo: 0.1% or more and less than 0.4% Ti: 0.003% or more and less than 0.1% V: 0.01% or more, 0.1 Less than% sol. Al: 0.002% or more, less than 0.2% N: 0.0010% or more, less than 0.020%, with the balance being Fe and inevitable impurities 1
When heated to 000 to 1350 ° C. and hot-rolled, the reduction ratio is set to 30% or more at 900 ° C. or more, and the finishing temperature is set to Ar ₃ to Ar ₃ + 150 ° C., followed by immediate quenching or air cooling. High temperature after reheating, characterized by being reheated to 880 ° C or higher and then quenched, then reheated to a temperature of 740 to 840 ° C and quenched, and subsequently reheated to a temperature of 700 ° C or lower and air-cooled. A method for manufacturing a structural fire-resistant steel material having excellent strength characteristics and a strength of 60 kg or more. 4. In weight% display, C: 0.05% or more and less than 0.20% Si: 0.1% or more and less than 2.0% Mn: 0.3% or more and less than 2.0% P : 0.03% or less S: 0.03% or less Mo: 0.1% or more and less than 0.4% Ti: 0.003% or more and less than 0.1% V: 0.01% or more, 0.1 Less than% sol. Al: 0.002% or more, less than 0.2% N: 0.0010% or more, less than 0.020% included Cu: 0.01% or more, less than 1.5% Ni: 0.02% or more , Less than 2.0% Cr: 0.05% or more, less than 1.5% B: 0.0005% or more, less than 0.005% Nb: 0.005% or more, less than 0.05% 1 type or When a steel containing two or more kinds and the balance consisting of Fe and unavoidable impurities is heated to 1000 to 1350 ° C. and hot-rolled, the reduction rate is set to 30% or more at 900 ° C. or more, and the finishing temperature is Ar ₃ ~ Ar ₃ +
After heating to 150 ° C, quench immediately or air cool 8
Reheat to 80 ° C or higher and then quench, then 740-840
Structural refractory having a strength of 60 kg or more, which is excellent in high-temperature strength characteristics after reheating, characterized by being reheated to a temperature of ℃, quenched and then reheated to a temperature of 700 ℃ or less and air-cooled. Steel material manufacturing method.